In general, a printed circuit board (“PCB”) refers to a component onto which various elements are mounted or electrically connected through integrated wiring. With technological development, the PCBs are being manufactured in various forms and with various functions including home appliances, communication devices, semiconductor devices, industrial devices, and electric vehicle control. As technological advances increasingly reduce the size of electronic components, PCBs are also becoming smaller, lighter, and higher value-added. Additionally, as the size of electronic components is reduced, PCBs are increasingly becoming multifunctional, with greater numbers of electronic components being connected on smaller and smaller PCBs.
A consequence of this multifunctional application is that the electronic devices consume more power, generating more heat. This heat generation can often determine user satisfaction and purchase criteria.
Conventionally, a multilayer PCB is manufactured by preparing a copper clad laminate (CCL) as a base substrate and accumulating a copper foil on which a circuit pattern is formed. The drawback of the convention copper (Cu) based multilayered PCB is that methods for increasing the efficiency of heat dissipation is limited.
Recently, aluminum (Al) based multilayer PCBs have been explored as a potential replacement to the Cu based multilayer PCBs, because Al has a higher thermal conductivity than Cu.
Japanese Patent Publication No. 2004-179291 discloses an example of an Al based PCB, which increases heat radiation efficiency and flexural strength by replacing the insulating layers with Al, and includes circuits disposed on both sides. Surface roughness is formed by through-hole processing. Also, the entire part is turned to a nonconductor. Al with both poles oxidized is brought into close contact with a coating layer of the through-hole, and circuits are formed on both sides of the Al. Both poles of the Al may be oxidized by depth of 10 to 100 μm. When the depth is 30 μm, the Al is not affected by electric shock and insulation efficiency is excellent.
A drawback of this approach is that a surface of the Al core may be corroded and undesired chemical reactions may occur during electrolytic reduction Cu plating, because Al has lower chemical resistance than Cu and is in an active ion state. The Cu layer generated by electrolytic reduction Cu plating may not completely achieve close contact with an Al core layer disposed under the Cu layer. Additionally, even after the Cu plating, a surface of the Cu layer may float due to a poor contacting force, accordingly reducing reliability of the product.
When the Al based PCB manufactured by the conventional method is used for office automation equipments, mobile terminals, and similar applications having an applied temperature range that is relatively narrow, the contacting force of the Cu layer may be stabilized by anodizing the Al core. However, when the Al based PCB is used in electronic control applications in vehicles, especially when mounting in an engine compartment, the applied temperature range is very large, resulting in degradation between an Al film and the Cu layer.
In addition, when the substrate is used for vehicles, the PCB may be damaged due to a difference in thermal expansion rate between the Al core and other layers disposed on the Al core.